How I can change the Username itself, not just the password.

As I say, the user ID is commonly known, it’s handled as public information. Every member of these forums knows the User ID of every other member. I can attempt to log in as anyone else, I get five attempts and I am then locked out from logging in (as anyone) for 15 minutes, with an e-mail sent to the person who I attempt to log in as. I know the login IDs of every person in my company. If I walk up to a computer that is at the lock screen and I press a key a message on screen will tell me that User-ID is currently logged in. If I repeatedly try to log in as that person the computer locks out for a period of time. If I go to the C:/Users directory of the PC I will see a list of all users who have successfully logged into this PC as the system has added profiles for them, the directory names are all the same as their User ID. I am not at all concerned that people in my company know my User ID for both General and Secret networks because I know that they don’t know my password. If I have network problems at work and I call the IT department, one of their first questions is ‘what is your User ID?’, they may have the ability to reset my password, but they have no visibility of my chosen password and will never ask for it. I am not concerned that people can attempt to log in as me in these forums, because I know that they don’t know my password, and will not guess it (it’s part pseudorandom, long, and contains a mixture of cases and special characters). Many trusted systems have default User IDs that cannot be changed, e.g. admin, root, administrator, sys, system. My point is that even high level trusted systems do not normally do anything to obscure/hide User Identification, and I can guarantee that even though my User ID is publicly known that information does not put people ‘half way’ to ‘cracking’ my account.